1. Field of the Invention
The present invention relates to radio frequency IC devices and methods of manufacturing the same, and, more particularly, to a radio frequency IC device preferably for use in an RFID (Radio Frequency Identification) system and a method of manufacturing the radio frequency IC device.
2. Description of the Related Art
In recent years, as a product management system, an RFID system has been developed in which a reader/writer for generating an induction field communicates with an IC tag (hereinafter referred to as a radio frequency IC device) attached to a product in a non-contact manner so as to obtain predetermined information stored in the IC tag. For example, Japanese Unexamined Patent Application Publication No. 2008-160874 discloses a radio frequency IC device used in an RFID system.
In a radio frequency IC device disclosed in Japanese Unexamined Patent Application Publication No. 2008-160874 (for example, see FIG. 5 in Japanese Unexamined Patent Application Publication No. 2008-160874), a flexible sheet including a feeding circuit provided thereon and a radio frequency IC chip mounted on the feeding circuit and another flexible sheet on which a radiation plate is disposed are bonded so that the feeding circuit and the radiation plate are capacitively coupled.
However, in this radio frequency IC device, high accuracy is required when bonding these flexible sheets. The accuracy is low, variations in the value of capacitive coupling between the radio frequency IC chip and the radiation plate occur and an impedance deviates from a set value. As a result, signal emission/reception performed by the radiation plate becomes unstable and signal transmission efficiency is reduced.